Conventional cooling systems do not exhibit significant reductions in energy use in relation to decreases in load demand. Air-cooled direct expansion (DX), water-cooled chillers, heat pumps, and even large fan air systems do not scale down well to light loading operation. Rather, the energy cost per ton of cooling increases dramatically as the output tonnage is reduced on conventional systems. This has been mitigated somewhat with the addition of fans, pumps, and chiller variable frequency drives (VFDs); however, their turn-down capabilities are still limited by such issues as minimum flow constraints for thermal heat transfer of air, water, and compressed refrigerant. For example, a 15% loaded air conditioning system requires significantly more than 15% power of its 100% rated power use. In most cases, such a system requires as much as 40-50% of its 100% rated power use to provide 15% of cooling work.
Conventional commercial, residential, and industrial air conditioning cooling circuits require high electrical power draw when energizing the compressor circuits to perform the cooling work. Some compressor manufacturers have mitigated the power inrush and spikes by employing energy saving VFDs and other apparatuses for step loading control functions. However, the current systems employed to perform cooling functions are extreme power users.
Existing refrigerant systems do not operate well under partially-loaded or lightly-loaded conditions, nor are they efficient at low temperature or “shoulder seasonal” operation in cooler climates. These existing refrigerant systems are generally required to be fitted with low ambient kits in cooler climates and other energy robbing circuit devices, such as hot gas bypass, in order to provide a stable environment for the refrigerant under these conditions.
Compressors on traditional cooling systems rely on tight control of the vapor evaporated in an evaporator coil. This is accomplished by using a metering device (or expansion valve) at the inlet of the evaporator which effectively meters the amount of liquid that is allowed into the evaporator. The expanded liquid absorbs the heat present in the evaporator coil and leaves the coil as a super-heated vapor. Tight metering control is required to ensure that all of the available liquid has been boiled off before leaving the evaporator coil. This can create several problems under low loading conditions, such as uneven heat distribution across a large refrigerant coil face or liquid slugging to the compressor, which can damage or destroy a compressor.
To combat the inflexibility problems that exist on the low-end operation of refrigerant systems, manufacturers employ hot gas bypass and other low ambient measures to mitigate slugging and uneven heat distribution. These measures create a false load and cost energy to operate.
Conventional air-cooled air conditioning equipment are inefficient. The kw per ton (kilowatt electrical per ton of refrigeration or kilowatt electrical per 3.517 kilowatts of refrigeration) for the circuits are more than 1.0 kw per ton during operation in high dry bulb ambient conditions.
Evaporative assist condensing air conditioning units exhibit better kw/ton energy performance over air-cooled direct-expansion (DX) equipment. However, they still have limitations in practical operation in climates that are variable in temperature. They also require a great deal more in maintenance and chemical treatment costs.
Central plant chiller systems that temper, cool, and dehumidify large quantities of hot process intake air, such as intakes for turbine inlet air systems, large fresh air systems for hospitals, manufacturing, casinos, hotel, and building corridor supply systems are expensive to install, costly to operate, and are inefficient over the broad spectrum of operational conditions.
Existing compressor circuits have the ability to reduce power use under varying or reductions in system loading by either stepping down the compressors or reducing speed (e.g., using a VFD). However, there are limitations to the speed controls as well as the steps of reduction.
Gas turbine power production facilities rely on either expensive chiller plants and inlet air cooling systems or high volume water spray systems to temper the inlet combustion air. The turbines lose efficiency when the entering air is allowed to spike above 15° C. and possess a relative humidity (RH) of less than 60% RH. The alternative to the chiller plant assist is a high volume water inlet spray system. High volume water inlet spray systems are less costly to build and operate. However, such systems present heavy maintenance costs and risks to the gas turbines, as well as consume huge quantities of potable water.
Hospital intake air systems require 100% outside air. It is extremely costly to cool this air in high ambient and high latent atmospheres using the conventional chiller plant systems.
Casinos require high volumes of outside air for ventilation to casino floors. They are extremely costly to operate and utilize a tremendous amount of water, especially in arid environments, e.g., Las Vegas, Nev. in the United States.
Middle eastern and desert environments have a high impact on inlet air cooling systems due to the excessive work that a compressor is expected to perform as a ratio of the inlet condensing air or water versus the leaving chilled water discharge. The higher the ratio, the more work the compressor has to perform with a resulting higher kw/ton electrical draw. As a result of the high ambient desert environment, a cooling plant will expend nearly double the amount of power to produce the same amount of cooling in a less arid environment.
High latent load environments, such as in Asia, India, Africa, and the southern hemispheres, require high cooling capacities to handle the effects of high moisture in the atmosphere. The air must be cooled and the moisture must be eliminated to provide comfort cooling for residential, commercial, and industrial outside air treatment applications. High latent heat loads cause compressors to work harder and require a higher demand to handle the increased work load.
Existing refrigeration process systems are normally designed and built in parallel. The parallel systems do not operate efficiently over the broad spectrum of environmental conditions. They also require extensive control algorithms to enable the various pieces of equipment on the system to operate as one efficiently. There are many efficiencies that are lost across the operating spectrum because the systems are piped, operated, and controlled in parallel.
Each conventional air conditioning system exhibits losses in efficiency at high-end, shoulder, and low-end loading conditions. In addition to the non-linear power versus loading issues, environmental conditions have extreme impacts on the individual cooling processes. The conventional systems are too broadly utilized across a wide array of environmental conditions. The results are that most of the systems operate inefficiently for a majority of the time. The reasons for the inefficiencies are based on operator misuse, misapplication for the environment, or losses in efficiency due to inherent limiting characteristics of the cooling equipment.